1. Technical Field
The present invention relates to a photoelectric conversion device.
2. Related Art
There have been known solar cells using polycrystalline, microcrystalline, or amorphous silicon. In particular, photoelectric conversion devices of laminated structure in which thin films of microcrystalline or amorphous silicon are laminated have been receiving attention, in view of resource consumption, cost reduction, and an increase in efficiency. In general, the photoelectric conversion devices are formed by sequentially laminating a first electrode, one or more semiconductor thin film photoelectric conversion cells, and a second electrode on a substrate whose surface has an insulation property. Each photoelectric conversion unit is composed of a p-type layer, an i-type layer, and an n-type layer laminated in that order from a light incident side.
As a method for increasing conversion efficiency of such a photoelectric conversion device, laminating two or more photoelectric conversion cells in a light incident direction has been known. On the light incident side of the photoelectric conversion device, a first photoelectric conversion unit including a photoelectric conversion layer with a wider band gap is disposed, and subsequently a second photoelectric conversion unit including a photoelectric conversion layer with a band gap narrower than that of the first photoelectric conversion unit is disposed. In this way, photoelectric conversion of incident light with a wide range of wavelengths can be achieved, to thereby improve the conversion efficiency of the device as a whole. For example, there has been known a structure in which an amorphous silicon photoelectric conversion unit (a-Si photoelectric conversion unit) is formed as a top cell, and a microcrystalline photoelectric conversion unit (μc-Si photoelectric conversion unit) is formed as a bottom cell.
Further, the photoelectric conversion device is often employed as integrated modules obtained by dividing the a-Si photoelectric conversion unit and the μc-Si photoelectric conversion unit into a plurality of rectangular cells by means of a laser and connecting the plurality of divided cells in series-parallel combination.
Meanwhile, in a state where a current generated in the μc-Si photoelectric conversion unit governs a current of each cell, currents are limited by a current that passes through a cell that is located in a region where a crystalline fraction of the μc-Si photoelectric conversion unit is lower in a plurality of series-connected cells. For this reason, there has been a problem in that it is impossible to enhance overall power production efficiency in the integrated modules of the photoelectric conversion device.